Electrically heated blanket



D 2, 1940- w. K. KEARSLEY 2,195,958

ELECTRICALLY HEATED BLANKET Filed Sept. 4, 1956 2 Sheets-Sheet 1 iInventor: William K. Kearsley.

H s Attorne g.

April 1940- w. K. KEARSLEY ELECTRICALLY HEATED BLANKET Filed Sept. 4,1936 2 Sheets-Sheet 2 Inventor: William K. Kearsley, yX/M 6 AWJ-M 4 HiAttorney.

Patented Apr. 2, 1940 UNITED STATES PATENT OFFICE William K. Kearsley,Schenectady, N. Y., alsignor to General Electric Company, a corporationof New York Application September 4, 1936, Serial No. 99,459

scum.

This invention relates to electrically heated blankets. and it has forits object the provision 'of an improved device of this character.

This invention contemplates the provision an improved electricallyheated blanket intended to take the place of blankets heretoforegenerally used in the home, in hospitals, etc.

These latter blankets generally are relatively heavy, and in very coldclimates, it is generally necessary to use so many of them that theweight becomes quite objectionable.

Moreover, it is a common experience for one to ilnd the bedroomrelatively warm when going to bed, and that the weight of the blanket orthe number required to give comfortable sleeping conditions at this timeis not nearly sumlcient to keep the sleeper warm later on in the nightwhen the room cools oil. If one wishes to be comfortable when firstgoing to bed, he must use a relago tively light covering and take thechance on waking up to provide more blankets as the room temperaturefalls. This practice is troublesome, and

at times, is actually dangerous in that it is conducive to colds.

This invention contemplates the provision of an improved electricallyheated blanket so light in weight as to be comfortable at the highestroom temperatures it is desired to use a covering at all, and ofsuitable means for adding suillcient heat energy to the blanket as theroom cools to maintain a comfortable temperature, irrespective of howlow the room temperature falls and irrespective of how it varies throughthe night.

In accordance with this invention. the blanket in one form thereof ismade of a suitable lightweight fabric, such as a cotton cloth. Attachedto the cloth is a suitable heating element. preferably in the form of aresistance conductor. The conductor is so distributed and arranged thatthe heat generated is distributed relatively uniformly throughout thearea of the blanket.

The temperature of the blanket is controlled by governing the heatenergy input to the blanket responsively to the ambient temperature ofthe 5 blanket, that is, in accordance with the temperature of the roomin which the blanket is located. In one form of this invention, thetemperature control means comprises a suitable temperature responsiveelement controlling a switch in the 5 heating circuit of the blanket toapply heat to and cut it oil from the blanket in accordance with thetemperature of the responsive element. The temperature responsiveelement is removed thermally from the blanket and is positioned in theroom to respond to the room temperature. In

addition to receiving heat from the room, the thermostat is arranged toreceive heat from a suitable auxiliary heating device arranged inthermal relation with it. The quantity of heat energy imparted to thethermostat by the auxil- 5 iary heating device and by the air in theroom determines the proportionate amount of time that the thermostatpermits the switch to supply heat to the blanket as compared with thetime that the heat is shut on. These time periods are varied 10 as theaction of the thermostat varies responsively to changes in the roomtemperature so as to hold a substantially constant temperature in theblanket.

Suitable means are provided for adjusting the 15 control device to holddiilerent temperatures in the blanket. In one form of this invention, asuitable indicating device is provided to assist in adjusting thetemperature. Preferably, the indicating device will be visible at nightso that a 20 person in a dark room can conveniently adjust the device tothe desired temperature.

For a more complete understanding of this invention, reference should behad to the accompanylng drawings in which Fig. l is a perspective 25view illustrating a portion of an electrically heated blanket arrangedin accordance with this invention, and illustrating a temperaturecontrol device therefor also arranged in accordance with this invention;Fig. 2 is a horizontal sectional view of the control device shown inFig. 1; Fig. 8 is a vertical sectional view of this control device: Fig.4 is a diagrammatic representation of the control device of Flgs. l. 2and 3, and of the blanket shown in Fig. l; and Fig. 5 is a view similarto Fig. 4 arranged to illustrate certain details of construction.

Referring to the drawings, this invention has been shown in one form asapplied to an electrically heated blanket III which is controlled bymeans of a'suitable temperature responsive ele- -ment II that isthermally removed from the blanket and arranged to respond to theambient temperature of the blanket. As shown in Fig. l. the blanketcomprises a pair of sheets l2 arranged 5 in superimposed relation andreceiving between them a resistance conductor II. The sheets ll may beformed of any suitable light-weight material, such as a soft plaincotton cloth, and the two sheets will be secured together inany sult- 5able manner as by stitching I at the periphery and where else in thebody of the pad that it is deemed advisable to use it to hold the sheetstogether. The resistance conductor it will have a suitable resistanceconducting element ll pro- 55 vided with an insulated water-proofcovering |1 formed of any suitable material, such as a suitablesynthetic rubber compound. The conducting element and covering are verylight and doed substantially uniformly throughout the area of theblanket I0. In other words, the resistance conductor is so arranged thatthe heat generated thereby is distributed uniformly over the blanketsurface whereby all portions of the blanket are maintained substantiallyat the same temperature. This, of course, is very desirable in that allparts of the bed will have substantially the same temperature. This isin striking contrast to the usual condition wherein the portions of thebed not in immediate contact with the body are cold. The resistanceconductor l3 may be and as shown is secured to the sheets |2 by stitches|1b looped over the conductor.

A suitable electrical terminal plug I! is attached to the blanket,preferably at one corner thereof, as clearly shown in Figs. 1, 4 and 5.This plug receptacle has a pair of terminal pins I9 connected to theends of the resistance conductor respectively and adapted to engage apair of contacts 20 in a supply plug 2| when the plug is applied, asclearly shown in Fig. 4. The plug 2| is connected to a supply plug 22 bymeans of a cord 23.

The temperature control device H for the blanket I0 is interposed in thecord 23 between the supply plug 22 and the plug 2| attached to theblanket, dividing the cord into two branches 23a and 23b.

This control device H, as shown more clearly in Figs. 1, 2 and 3,comprises an outer casing 24 which may have any suitable shape, butwhich preferably will have a rectangular box-like form, as shown inFig. 1. The casing 24 may be formed of any suitable material, such aspressed steel or wood. Housed within the casing 24 is a suitable switch25 adapted to be connected in the heating circuit of the pad. The switch25 may have any suitable construction, but preferably will be of thesnap action type. The switch is mounted upon a base 25a mounted in therear of the casmg.

The switch 25 has a housing or casing 26 in which is mounted a movablecontact 21 (Fig. 4) arranged to cooperate with a fixed contact 28.Contact 21 is carried by a suitable flexible switch arm 29 formed ofconducting material, and rigidly secured at one end to a fixed support33 mounted in the housing and at its other end rigidly secured to thecontact 21. Arranged on opposite sides of the flexible switch member 29are a pair of springs 3| secured to the movable contact 21 at one endand at their opposite ends are received in knife-edge bearings 32. Themembers 3| are in longitudinal compression thereby putting the switcharm 29 under tension. The springs 3| normally bias the movable contact21 away from the fixed contact 28. A suitable stop 33 is provided tolimit the movement of the contact arm away from the fixed contact. Themovable contact arm. 29 when moved to the left, as viewed in Figs. 4 and5, snaps through a neutral position to close the contacts. However, ifthe force which moves the switch arm 29 to the closed position isrelieved, the switch will automatically move with a snap action to itsopen position. The

, plunger 33a.

switch arm 29 is moved to its closed position by means of a plunger 33a.protruding from the casing 23, as shown in Fig. 3.

As shown, diagrammatically in Figs. 4 and 5, one conductor of the supplycord section 23a connects one side of the heating element l3 to thefixed contact 24. From here, the circuit through the control device maybe traced from the switch arm 29 when the switch is closed through theplate 30, which is conducting, and to one side of a transformer 33bmounted in the casing 24; the function of this transformer will bedescribed in gfieater detail hereinafter. The other conductor of thesection 230 connects the other side of the heating element to theopposite side of the transformer.

The switch arm 29 is controlled by means of a bimetallic thermostat bar34. This bar, it will be understood, is formed of two metals havingdisimilar coeiiicients of expansion, such as Invar and brass securedtogether lengthwise in any suitable manner, as by welding. Thebimetallic bar 34 is positioned on the rear of the casing 24, as shownin Figs. 2 and 3, having one end rigidly secured to the back of the base25a by means of screw fastening means 35 and its other end free to movein response to changes in temperature. Preferably, a metallic plate 34will be mounted on the rear of the base, and preferably, thethermostatic bar 34 will be arranged on the outside of this plate insubstantially parallel relation with it. A suitable stud or rod 31 isinterposed between the free end of the bimetallic thermostat bar and theswitch operating The rod 31 enters the casing 24 through an apertureprovided for it in the plate 36, and abuts the end of the plunger, asshown in Figs. 3, 4 and 5.

The bimetallic bar 34 is so arranged that it will move outwardly fromthe casing upon an increase in temperature and toward the casing upon adecrease in temperature, and when its temperature is below apredetermined minimum it applies a sufliclent force to contact arm 29 tohold the switch closed. When the temperature of the bar rises to apredetermined maximum, it will have moved outwardly sufiiciently topermit the switch to open. Conversely, when it cools to thepredetermined low temperature, it will have moved inwardly sufficientlyto close the switch. Preferably, the bimetallic thermostat bar 34 willbe inclosed by means of a suitable relatively thin casing member 38secured to the base plate 250.

The adjustment of temperature of the control device is effected bychanging the position of the switch 25 in the casing 24. This isaccomplished by mounting the switch member for pivotal movement. Forthis purpose, the switch 25 is mounted in a suitable saddle or support39 which at its lower right hand corner, as viewed in Fig. 3, is mountedupon pins 40 which in turn are mounted on a suitable supporting bracket4| in the casing. Preferably, the bracket 4| will be attached directlyto the base plate 25a at the rear of the casing, as shown in Fig. 3. Itwill be observed that the switch because of the location of the pivotpins 40 always tends to move in a counter-clockwise direction, as viewedin Fig. 3, under the influence of gravity.

Threaded in the bracket 4| is an adjusting screw 43 having its inner endbearing against the saddle 39. It will be clear that the position of theswitch 25 in the casing is varied when the position of the screw ischanged. When the screw 43 is turned outwardly to permit the switch 25to move in a counter-clockwise direction, as

ting of the device. Conversely, when the screw 48 is turned inwardly tomove the switch in the opposite direction it increases the temperaturesetting of the device. The adjusting screw projects outwardly from thefront wall of the casing through a suitable aperture provided for it inthis wall, and on the projecting end of the screw there is a suitableknob 44 whereby the screw can be conveniently adjusted.

In view of the foregoing, it will be observed that the bimetallicthermostat bar responds to the temperature of the room in which thecontrol I I is placed. In addition to this, the thermostat bar is causedto respond to a local heat source which is obtained by winding thethermostat bar with an auxiliary resistance conductor 45. Preferably,the two side edges of the bimetallic thermostat bar will be providedwith U-shaped insulating coverings 40 about which the resistanceconductor is wound. The auxiliary heating coil 45, as shown, isconnected at one side to one side of the transformer lib and at theother side to the switch contact 28 so that when the switch is closed,the heating coil is energized, whereas when the switch is opened thecoil is deenergized.

The electrical energy input to the blanket I0 is controlled by theproportion of time that the switch 25 is closed to the time it is open.These times are controlled by the temperature of the thermostat barwhich is Jointly dependent upon the auxiliary heater 4! and the roomtemperature. The heat applied by the auxiliary heater 45 to thethermostat bar is delivered at a constant rate, whereas that supplied bythe room is variable. For a given unchanging room temperature, thethermostat controls the switch 25 to deliver an invariable amount ofenergy to the blanket which then delivers a constant heat energy. Underthese conditions, the temperature of the blanket is constant. When theroom temperature varies, however, the heat energy delivered by theblanket changes. Thus, if for a given setting of the thermostat, theroom temperature should decrease, the heat that will be imparted to thethermostat bar from the room is reduced and it will require a longerperiod of time for the auxiliary heater 45 to heat the bar 34 to thetemperature at which it opens the switch than it did before; and afterthe switch has been opened and the auxiliary heater 4! is deenergized,the thermostatic bar I4 will cool quicker to reclose the switch due tothe increased cooling action of the room. The two .actions in delayingthe opening of the switch and in advancing its closing, cooperate toincrease the proportion of time that the switch is closed. In otherwords, as the room cools, a greater amount of energy is supplied to theblanket III to hold its temperature constant in spite of the decrease inroom temperature. Conversely, when the room warms up, the proportion ofthe time that the switch is closed to the time that it is opened isreduced so as to reduce the energy input of the blanket sumciently tohold a constant temperature. The ioregoing control is very importantbecause it provides an energy input to the blanket which is inverselyrelatedto the temperature of the room.

It is to be understood that the control is so arranged that asubstantially uniform temperature is maintained in the blanket for anygiven setting of the control device, irrespective oi variations in theroom temperature. The temperature of the blanket ll can be adjusted toany suitable value by the knob 44. However, for any given setting, theinverse relati between the energy input to the blanket and thetemperature of the room is maintained by the control device. Moreover,it will be clear that the blanket temperature will remain substantiallyuniform irrespective of variations in the voltage of the electricalsupply source. Should the voltage drop below the normal, the voltagewill drop in the auxiliary heater 4 5, and as a result, it will functionto increase the proportion of the time that the switch is closed to thetime that it is open to compensate for the dip in line voltage.Conversely, should the supply voltage increase above the normal, thecontrol will function to decrease the proportion oi time that the switchis closed to the time that it is open to compensate for the voltagerise. I

A suitable indicating device is provided to assist in adjusting thetemperature of the con- Interposed between the window may be green,whereas the member 50 may be 86 red. They may be formed of pieces ofglass, Celluloid or like materials. The members 4| and 50 are mountedupon asuitable carriage Ii which supports them in substantially the sameplane and in a plane substantially parallel to the plane of the window41. The carriage II at its upper end is pivotally attached to a link 62which has afixed pivotal connection 53 with the base 25a. The lower endof the carriage BI is secured to a bracket arm 54 which is rigidlysecured to the saddle 39 of the switch. Thus, when the switch saddle 30is moved on the pivot 40, the carriage Si is moved vertically oi thecasing so as to move the colored members 49 and 60 vertically in thecasing. Preferably, the line 55 (Fig. 4) defined by the meeting edges ofthe colored members 48 and 80 will be perpendicular to the line ofmovement of the colored members.

It will be observed in view of the foregoing arrangement that when theadjusting knob 44 is turned to set the temperature of the controldevice, the colored members 48 and I! are moved so that one or the otheror a part of each will appear in the field of vision of the window 41.The parts are so arranged that on the very low temperature settings ofthe device, the green member 49 alone will appear in the window, and asthe temperature setting is raised the green color will advance upwardlyand eventually the red color will enterthe field of vision. As thetemperature settings increase, the meeting line 55 of the two colorswill be elevated on the field of vision, the increasing amount of redappearing denoting an increasing temperature setting. At the very hightemperature settings, the green color will have disappeared and the redonly will show.

The lamp 48 as shown in Fig. 4, is connected to the two sides oi thetransformer 38b and is continuously energized while the device isoperating. Preferably, a suitable resistance 56 will beinserted in thlamp circuit as a protective device.

It is preferable that a suitable control switch 51 (Fig. 4) be mountedin the casing 24 and connected in the energizing circuit of the blanketto open and close this circuit, as desired. This switch preferably willbe of the snap action type and will have a control member 58 (Fig. 1)accessible on the exterior of the casing for convenience of operation.

At times, it is desired to operate the blanket on a relatively lowvoltage in order to eliminate dangerof shocks, and it is for thispurpose that the transformer 33b is provided. The transformer isarranged to reduce the voltage of the supply source attached to the plug22 to the desired low value. Where this low voltage is not desired, thetransformer is omitted. As shown in Fig. 2, where the transformer isused it is preferable to ventilate the casing so that the thermostat 24will not be influenced by heat generated in the transformers. For thispurpose screened windows 59 are provided in the end walls of the casing.The wall a also thermally insulates th transformer 23 from thethermostat.

If desired, and it is generally preferable to do so, a suitable numberof protective devices 60 will be incorporated in'the blanket and will beconnected in series with its heating circuit, as shown in Fig. 4. Thesedevices may be any suitable thermostatic devices arranged to open theheating circuit in case of an abnormal high temperature condition, suchas a temperature of 180 to 200 F.

It will be observed that I have provided an electrically heated blanketwhich is very light in weight, and which is arranged to heat all partsof the bed inasmuch as the heat energy developed in the blanket isuniformly distributed. Moreover, it will be observed that I haveprovided a temperature control for the'blanket arranged to vary the heatenergy input to the blanket inversely with variations in the roomtemperature so that as the room cools of! during the night, the heatenergy input to the blanket is increased, and conversely, if the roomshould become warm the heat energy will be reduced, all to hold asubstantially uniform temperature in the blanket.

Moreover, I have provided a temperature control which embodies animproved visual signal so that the device can be readily adjusted in thedark at any time during the night if it is found desirabl to do so.

This invention is particularly applicable also to airplanes, trains,ships and the like where individual sleeping compartments are provided.In such applications a separate blanket l0 and control H will beprovided for each compartment, the control being located so as torespond to the temperature of the air in the vicinity of the sleepingperson. Where a low voltage operation is desired, separate transformers331) may be used, as shown in the drawings, or one transformer may beused for the whole system.

While I have shown particular embodiments of my invention, it will beunderstood, of course, that I do not wish to be limited thereto sincemany modifications may be made, and I, therefore, contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention.

What I claim is new and desire to secure by Letters Patent of the UnitedStates:

1. In an electrically heated blanket for a bed, a temperature controldevice for said blanket comprising a temperature responsive element outof heat conducting relation with said blanket and responding to the airtemperature of the bed room in which the blanket is placed controllingthe energy input to the blanket to vary it in the inverse order withvariations in said air temperature so that a substantially constanttemperature is held in said blanket irrespective of said variations insaid air temperature.

2. An electrically heated blanket having a heating circuit and atemperature control device comprising a switch connected in the heatingcircuit of said blanket, a temperature responsive element for operatingsaid switch to shut oil and reapply energy to said blanket, thetemperature responsive element being thermally removed from theinfluence of the temperature of said blanket and exposed to the airtemperature of the room in which the blanket is located, an auxiliaryheating element also thermally removed from the influence of thetemperature of said blanket arranged to apply heat locally to saidthermostatic switch in addition to that received from said air of saidroom, the auxiliary heating element being connected in said heatingcircuit of said blanket so as to be energized and deenergized when saidcircuit is energized and deenergized, the heat imparted to saidtemperature responsive element by the air of the room and said auxiliaryheating element Jointly controlling the operation of said temperatureresponsive element to operate the switch to vary the energy input to theblanket in the inverse order 'with variations in said air temperature soas to hold a substantially constant temperature in the blanketirrespective of said variations in said air temperature.

3. An electrically heated blanket comprising a blanket formed of a lightweight material, a heating element associated with said blanket, anelectrical supply circuit for said heating element, a thermostaticswitch connected in said supply circuit movable between controllingpositions to open and close said supply circuit responsively toincreases and decreases in temperature, said thermostatic switch beingout of heat conducting relation with said blanket and responding to thetemperature of the room in which said blanket is located, an auxiliaryheating element connected in said supply circuit arranged to apply heatlocally to said thermostatic switch only when said switch is in itscontrolling position to close said supply circuit so ing having anoperating element to open and close said switch, a temperatureresponsive element engaging said operating element to open and closesaid switch depending upon the temperature of said temperatureresponsive element, an adjusting screw in said casing for adjusting theposition of said switch and thereby the tempcratures of said temperatureresponsive element at which said switch is opened and closed, a knobaccessible on the exterior of said casing controlling the position ofsaid screw, a window in a wall of said casing, a lamp in said casingback of said window, a pair of transparent members in said casing havingdifferent colors arranged substantially in the same plane and parallelto said window between the window and said lamp, means supporting saidmembers for movement in said plane across the field of vision defined bysaid window, and a bracket connecting said switch with said coloredmembers arranged to move said members in said field of vision when theposition of said switch is ad- J'usted.

5. A temperature control device comprising a. casing, a pivotallymounted switch in said casing having an operating element to open andclose said switch, a temperature responsive element on the exterior ofsaid casing to respond to the ambient temperature thereof, a memberoperated by said temperature responsive element entering said casing andengaging said operating element of said switch to open and close saidswitch depending on the temperature of said temperature responsiveelement, an adjusting screw in said casing for adjusting the position ofsaid switch and thereby the temperatures of said temperature responsiveelement at which said switch is opened and closed, a knob accessible onthe exterior of said casing controlling the position of said screw, awindow in a wall of said casing adjacent said knob, a lamp in saidcasing back of said window, a pair of transparent members in said casinghaving difi'erent colors arranged in substantially the same plane andparallel to said window between the window and said lamp, meanssupporting said members for movement in said plane across the field ofvision defined by said window, and a bracket connecting said switch withsaid colored members arranged to move said members in said field ofvision when the position of said switch is adjusted.

6. A temperature control device comprising a switch having cooperatingrelatively movable contacts, a housing for said contacts, a plungerentering said housing cooperating with the contacts to control therelative movement between said contacts, a temperature responsiveelement controlling the operation of said plunger, means mounting saidhousing for movement to vary the position of said plunger with referenceto said temperature responsive element, and means for adjusting theposition of said housing.

7. A heat control device for an electrically heated blanket and the likecomprising a housing, a thermally insulating wall closing one side ofsaid housing, a switch in said housing adapted to control the energizingcircuit of said blanket, a thermostatic element mounted outside of saidwall and having an operating connection through the wall with saidswitch to operate the switch responsively to the temperature changes insaid thermostatic element, a voltage reducing transformer within saidhousing arranged to be connected in said energizing circuit, and windowsin said housing to ventilate it and carry away heat generated in saidtransformer, the ventilation of said housing and said thermallyinsulating wall preventing a transfer of heat from the transformer tothe thermostatic element whereby the latters temperature is uninfiuencedby the heat generated in said transformer.

8. An electrically heated blanket for a bed comprising a blanket, aheating element for applying heat to said blanket, and a temperaturecontrol device for said blanket having control means for controlling theelectrical energy input to said heating element and a bimetallictemperature responsive device out of heat conducting relation with saidblanket and exposed to the air temperature of the compartment in whichsaid blanket is functioning operating said control means so as to varysaid energy input to said heating element in the inverse order withvariations in said air temperature so that a substantially constanttemperature is held in said blanket irrespective of said variations insaid air temperature.

WILLIAM K. KEARSLEY.

